The present invention relates to pot-broaching slots at the circumference of a workpiece, to leave radially outwardly extending teeth or ribs between the slots.
The broach in the machine is generally tubular and is provided at its interior with a multiplicity of rows of cutting teeth, the teeth in each row being of increasing height to cut slots progressively as the workpiece moves relative to the broach longitudinally thereof.
Pot broaching machines may have vertical or horizontal broaches, either the broach or workpiece may be moved relative to the other, and if the workpiece is moved, it may be pushed or pulled through the workpiece. The slots and teeth formed by broaching may be parallel or helically inclined to the axis of the piece. In the illustrated embodiment, a push-up vertical broaching machine is shown, designed to cut slots parallel to the axis of the workpiece and broach.
One of the advantages of broaching is that, properly performed, parts are broached to substantially the accuracy provided for the broach teeth. This assumes of course that the workpiece is accurately guided through the broach. This in turn has been accomplished in the past by providing guide surfaces in the broach which extend parallel to the broach axis, and in using the crests of the teeth or ribs left on the workpiece as the slots are progressively deepened which slide on guide surfaces in the broach which are intermediate adjacent rows of cutting teeth and which extend parallel to the broach axis.
While this has proved perfectly satisfactory in most cases, it sometimes happens that a workpiece is formed of a material or is of a shape which is not suitable to provide the required guiding sliding contact with the broach.
In accordance with the present invention, this difficulty is overcome by providing a pusher having teeth which register with the teeth or ribs of the workpiece as they are formed by broaching slots, the teeth of the pusher having radially outwardly facing crests which slide on axially extending guide surfaces in the broach. The crests of the pusher teeth are located at a diameter slightly larger than the original diameter of the workpiece or the OD of the finished workpiece so that the crests of the teeth or ribs on the workpiece remain.
The pusher is shaped to conform to locating surfaces on the broach so that as the pusher is guided accurately through the broach, so also is the workpiece.
In addition, to insure against circumferential drift as the workpiece moves through the broach, the pusher and broach have cooperating rib and slot guide portions, shown herein as provided by a rib or finger in the pusher received in a guide slot in the broach.
In Riggio et al, U.S. Pat. No. 3,162,089, there is shown a pot broach in which a circular blank is moved through the broach by a toothed forcing head, but the annular die blocks which are assembled to form a pot broach, have central internally toothed openings and which are said to be "-accurately the diameter of the finished gear-its teeth tip diameter." He describes the tips of the forming gear tooth as riding the bores of the blocks to accurately guide and center the blank.